Middle English word bak comes from Proto-Indo-European *bʰog-, Proto-Indo-European *bhAg-, Proto-Indo-European *bʰeg-, Proto-Indo-European *bʰogo, and later Proto-Germanic *bakiz (Beach, strand. Brook, stream.)
| Dictionary entry | Language | Definition |
|---|---|---|
| *bʰog- | Proto-Indo-European (ine-pro) | flowing water, flowing water, brook, stream, flowing water, stream |
| *bhAg- | Proto-Indo-European (ine-pro) | |
| *bʰeg- | Proto-Indo-European (ine-pro) | to break |
| *bʰogo | Proto-Indo-European (ine-pro) | |
| *bakiz | Proto-Germanic (gem-pro) | Beach, strand. Brook, stream. |
| *bakjaz | Proto-Germanic (gem-pro) | |
| *bankiz | Proto-Germanic (gem-pro) | A raised surface; bulge; hillock; slope. Bench. |
| *baką | Proto-Germanic (gem-pro) | Back, rear. |
| bekkr | Old Norse (non) | Brook, creek. |
| bæc | Old English (ang) | (anatomy) back. Back or rear end (of something). |
| bak | Middle English (enm) | Animal fur or pelt. Back. Bat (flying rodent). |